Christianity must be the first religion to teach its members about what its faith is. It has an authoritive textbook, the Bible, and Martin Luther believed very deeply that God is a personal God and every one should know God by personally studying the Bible. This brought about the Reformation and the beginning of the acquisition of knowledge.
Of course the interpretation of the Bible can sometimes be divisive. This is unavoidable for God is trying to speak to humankind who is imperfect. So our understandings are skewed by our background, our culture, and our bias. Actually most Christian groups do agree on the fundamentals of the faith. We are all unified by a Christian creed formulated by the earlier church fathers, normally referred to as the Apostle's Creed. The only differences we have are the nitty-gritties - the organisation structures, the form the rituals are supposed to be performed, and the "I am more saintly than you" complex.
Present day Christians normally do not have any problem attending each other's Sunday services, or participating in each other's sacraments (commemorative rituals instituted in the Bible). Most of the time we chose a particular denomination because we found God through that denomination, or we found the format of service more helpful to us, or because it is nearest to our residence.
Of course it is not realistic to expect all denominations to integrate into one Christian church. Maybe the last phrase is not appropriate, as all churches believed that every denomination, every little Christian gathering throughout the world, is part of the Universal Church, the one Christian Church. Christians when reciting the Apostle's Creed, would say, "I believe in the Universal Church, the fellowship of all Christians."
I believed that denomination is God's aggressive strategy for spreading His message. He will call fervent believers, free them from the shackles of church authorities, and launched them to spread the gospel based purely on their faith in God. The Methodist denomination was a child of an Anglican priest, now it has grown to be as big as his parent. So the church rejuvenates itself through the birth of denominations. They are a blessing to the Universal Church.
Today, I have not come across a church, that recites the Apostle's Creed, preaching against another church, although others might have this experience. Yes some churches might criticize another church. Some churches even do so with other churches within their own denomination. All of us are humans, even the religious leaders, and as long as we all hold on to the principle that the Bible has the final word our prejudices will never grow out of proportion. A perfect Universal Church will come one day, let not the denominations worry too much over this.
First we will have a new heaven and a new earth where God will dwell with all His people. There will no more be denominations, for there is only one temple, The Lord God Almighty.
When the world think about the divisiveness of Christianity, the fighting in Northern Ireland will naturally come up. Let all Christians pray for peace in Ireland to remove this shameful reflection on Christianity. I will not even call it a stain. It is just a mirage. The fighting in Ireland is not about Christian doctrines. It is an ethnic struggle by two different groups, which so happen are identified with two distinct denominations. It is not a religious struggle it is a political struggle where the groups find it easier to galvanise the people using religious sentiment to keep their struggle alive.
Many people have found this a potent weapon. Politics has such a corrupt intoxication on some that they will do any thing, use any weapon, and preach any doctrine to achieve their goal. The struggle in Northern Ireland is not a war between Christians, in as much as the destruction of the World Trade Centre on September 11 is a war between Christianity and Islam. It is so sad to see humankind making use of God for their own end. To me it is worst than selling out their parents for a fast buck. I am very sure that such blasphemers will never see God after their death.
